1. Field of the Invention
This invention relates to hypersonic vehicles and in particular, to a system for minimizing temperature gradients across basic internal structure stiffening members of such vehicles by circulating controlled temperature fluid through central ducts built into the same.
Hypersonic aerospace vehicles such as the Space Shuttle, NASP and the projected Mach 3 to 5 Civilian Transport Aircraft experience rapid and extreme changes in skin temperature as they exit and enter lower earth atmosphere. Correspondingly, temperatures drop to quite low levels during orbital or ecto-atmospheric operations.
Fuselage internal structural elements and external skin panels experience temperature excursions of from -400 degrees to +1600 degrees Fahrenheit with the skin panels sometimes seeing these 2000 degree changes over a 30 minute trajectory.
2. Description of the Prior Art
As a result of more powerful engines, easy accessibility to high specific impulse fuels such as liquid hydrogen and exotic monopropellants and growing needs for single stage to orbit travel, hypersonic vehicles have been designed with a variety of thermal protection systems allowing for speeds of up to Mach 25 without damage to structure by frictional heating from atmospheric gases.
Space Shuttle's tiles and Apollo's ablative nose heat shield are typical of high speed friction adaptive technology. More recent uses of structural cooling means have been disclosed such as those in U.S. Pat. No. 4,786,015 to Niggeman defining a hollow tube conduit system for conductive transfer of heat from structure members to heat exchanger surfaces, and U.S. Pat. No. 4,273,304 by Fosch/Lawning, et al, for a heat removal system using heat pipe means to cool the actual vehicle structure. Neither of these, nor any other found in a search of the literature, provides for the structural element temperature normalizing feature of the within invention. The normalizing system provides heating and cooling, as required, to eliminate thermally induced stresses in individual structural members caused by the extremes of temperature difference between outer skin panels supported by an outer load bearing surface of such members and the internal systems supported by an inner load bearing surface.
Because of temperature gradients across the radial span of the support element, thermal expansion at the extremes of temperature can induce appreciable strain in the member itself, depriving it of strength needed for support and stresses induced by maneuvering or high acceleration profiles of takeoff and descent.
U.S. application Ser. No. 248,687, Integral Structure and Thermal Protection System, assigned to the assignee of the within invention, describes an innovative integrated skin panel/internal structure system for minimizing the effects of high external skin temperature on primary vehicle structure supporting such panels. While each of the above references seeks to protect basic vehicle structure from external or skin conducted high temperatures, none utilizes the temperature normalizing equipments and concepts of this invention wherein a temperature conditioner fluid, not necessarily for cooling only, is used to normalize temperatures across the member to reduce internal stresses caused by thermal differences.